Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 140200
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1000 PM EDT SAT SEP 13 2014

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN JUST TO OUR SOUTH OVER THE WEEKEND
AND INTO EARLY NEXT WEEK WITH HUMID AND UNSETTLED WEATHER EACH DAY.
A BACK DOOR COLD FRONT WILL THEN CROSS THE AREA BY THE MIDDLE OF
NEXT WEEK WITH A COOL AIR WEDGE PATTERN SETTING UP BY THE END OF THE
WORK WEEK.

&&

.NEAR TERM /THROUGH SUNDAY/...
0200 UTC UPDATE...POPS WERE ADJUSTED TO FIT THE LATEST RADAR
TRENDS...FAVORING A SWATH FROM SPARTANBURG TO CHARLOTTE. SKY COVER
WAS UPDATED FROM SATELLITE IMAGERY...INTRODUCING BREAKS IN THE NORTH
AND WEST.

AT 900 PM EDT SATURDAY...A BROAD LOW AMPLITUDE UPPER TROUGH WAS
LOCATED OVER THE NORTHERN TIER OF STATES...WITH ZONAL FLOW ACROSS
THE NATION. MODEL DATA SHOWED A WEAK UPPER IMPULSE CROSSING THE
SOUTHERN APPALACHIANS THIS EVENING. SURFACE ANALYSIS PLACED A
STATIONARY FRONT NEAR THE FALL LINE IN THE PIEDMONT OF THE CAROLINAS
AND GA.

MOST CONVECTIVE ACTIVITY HAS BEEN CONCENTRATED CLOSE TO THE SURFACE
FRONT IN THE SC MIDLANDS. OUTFLOW BOUNDARIES MOVING NW FORM THIS
AREA HAVE REACHED THE SOUTHERN PORTION OF THE CHARLOTTE METRO
AREA...BUT APPEAR TO BE SLOWING. ANOTHER ROUND OF CONVECTION MOVING
SOUTH ACROSS THE US 74 CORRIDOR IN THE NC FOOTHILLS APPEARS TO BE ON
A COLLISION COURSE WITH THE CHARLOTTE AREA STORMS. MORE CONVECTION
WAS NOTED IN NE GA...AND THE SW NC MOUNTAINS.

MODEL SOUNDINGS SHOW INSTABILITY WANING THIS EVENING...BUT WITH A
VERY MOIST PROFILE...WEAK STEERING FLOW...AND BOUNDARIES COLLIDING
AND WANDERING ABOUT...HEAVY RAINFALL AND LOCAL FLOODING MAY CONTINUE
WELL INTO THE NIGHT. NE WINDS BEHIND THE FRONT MAY BE TO LIGHT TO
KEEP FOG FROM FORMING...BUT GUIDANCE ONLY SUPPORTS VERY LOW
VISIBILITY IN THE NC MOUNTAIN VALLEYS. MINIMUM TEMPERATURES WILL RUN
NEAR NORMAL IN RELATIVELY COOL NE FLOW.

COOL HIGH PRESSURE WEDGING DOWN THE EAST SLOPES OF THE APPALACHIANS
WILL CONTINUE THROUGH SUNDAY. LOOKS LIKE CLOUDS WILL BE PLENTIFUL...
BUT ISENTROPIC LIFT OVER THE WEDGE LOOKS WEAK...SO PRECIP CHANCES
ARE ON THE LOW END FOR SUNDAY. THE SW HALF OF THE AREA STANDS THE
BEST CHANCE FOR SOME PATCHY LIGHT RAIN...AND EVEN SOME SCT
SHOWERS/THUNDERSTORMS OVER THE SW MOUNTAINS WHERE THE WEDGE AIRMASS
TYPICALLY DOES NOT REACH. IT WILL BE A COOL DAY ON SUNDAY WITH
MAX TEMPS UP TO 15 DEGREES SHY OF CLIMO OUTSIDE THE MOUNTAINS.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 210 PM SATURDAY...WE APPEAR TO HAVE ENTERED INTO A PERIOD OF
TIME WHEN COLD AIR DAMMING WEDGES WILL WAX AND WANE AS THE OVERALL
UPPER PATTERN REMAINS FAIRLY CONSTANT...WHILE AN OLD SURFACE
BOUNDARY REMAINS STRUNG OUT W TO E TO OUR SOUTH AND HIGH PRESSURE
CENTERS PASS BY TO OUR N. THE PROBLEM IS THAT EACH PASSING HIGH
STAYS PROGRESSIVE...SO THE WDEGE NEVER REALLY LOCKS IN. THE FIRST
SUCH WEDGE ON SUNDAY NIGHT WEAKENS AND FALLS APART ON MONDAY AS WHAT
PASSES FOR A PARENT HIGH DRIFTS OFF THE NE COAST AND WEAKENS FURTHER
AND A LEE TROF ESSENTIALLY OVERWHELMS THE REMNANT COOL POOL E OF THE
MTNS. AFTER MILD OVERNIGHT TEMPS...THIS SHOULD ALLOW FOR SOME
REBOUND OF HIGH TEMPS ON MONDAY ASSUMING THE COOL POOL DRAINS AND WE
GET SOME AFTERNOON SUN ACROSS THE FOOTHILLS AND PIEDMONT. HAVE
CONTINUED A DOWNWARD TREND ON PRECIP CHANCES BASED ON THE NEW MODEL
GUIDANCE AND 09Z SREF.

ON MONDAY NIGHT...A FAIRLY STRONG SHORT WAVE WILL MOVE OVERHEAD
WHICH WILL SERVE TO BRING THE AXIS OF A BROAD UPPER TROF OVER THE
CAROLINAS FOR TUESDAY. THE APPROACH AND PASSAGE OF THIS WAVE MAY
TRIGGER ADDITIONAL SHOWER ACTIVITY OVERNIGHT SO A CHANCE POP WAS
KEPT ACROSS MOST OF THE REGION THROUGH TUESDAY MORNING. THIS FEATURE
WILL ALSO BRING A REINFORCING SURFACE BOUNDARY IN FROM THE WEST
WHICH SHOULD PUSH THROUGH EARLY IN THE DAY. BEHIND THIS
BOUNDARY...THE NEXT SURFACE HIGH SHOULD BRIDGE ACROSS THE
APPALACHIANS ON TUESDAY SETTING UP THE POTENTIAL FOR THE DEVELOPMENT
OF ANOTHER WEDGE-LIKE SCENARIO BY THE END OF THE DAY. THE GFS IS
MOST AGGRESSIVE WITH DEVELOPING NEW PRECIP IN THE DEVELOPING
EASTERLY UPSLOPE IN THE AFTERNOON BUT EVEN THE NAM HAS SOME ACTIVITY
NEAR THE MTNS. WILL NUDGE THE FCST IN THE DIRECTION OF THE LOWER POP
SEEN IN THE NEW MOSGUIDE AND AWAY FROM THE MORE ROBUST SREF. TEMPS
COULD BE TRICKY AGAIN IF NEW PRECIP DEVELOPS PER THE GFS. EXPECT
TEMPS TO BE A BIT WARMER ACROSS THE SOUTH BUT KEPT THEM THE SAME
ACROSS THE NRN TIER.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
AS OF 155 PM SATURDAY...THE MEDIUM RANGE FCST PICK UP AT 00Z ON
WEDNESDAY WITH A BROAD...LONGWAVE UPPER TROF OVER THE EASTERN CONUS
AND UPPER RIDGING OVER THE WEST. THE TROF IS EXPECTED TO AMPLIFY TO
SOME DEGREE OVER THE NEXT COUPLE OF DAYS AND THEN LIFT NE BY THE END
OF THE WORK WEEK. BY NEXT WEEKEND...THE UPPER RIDGE WILL BUILD
EASTWARD AND LIKELY BE IN PLACE OVER THE FCST AREA BY NEW DAY 7.

AT THE SFC...A NORTHERN PLAINS HIGH WILL DRIFT FARTHER EAST ON TUES
AND SHOULD BE CENTERED OVER THE GREAT LAKES BY THE START OF THE
MEDIUM RANGE AT 00Z WED. THE MODELS CONTINUE TO INDICATE THAT THIS
HIGH WILL BE ABSORBED BY A STRONGER CANADIAN HIGH BY LATE WED/EARLY
THURS. THE HIGH WILL THEN DRIFT OVER NORTHERN NEW ENGLAND OVER THE
NEXT DAY OR TWO AND REMAIN THERE THRU NEW DAY 7. AT THE SAME
TIME...BOTH THE GFS AND ECMWF TRY TO SPIN UP A SFC LOW JUST OFF THE
CAROLINA COAST WHICH ACTS TO ENHANCE/STRENGTHEN A COLD AIR WEDGE PUT
IN PLACE BY THE NEAR STATIONARY SFC HIGH TO THE NE. THE CONSENSUS
AMONG THE GFS...ECMWF...AND CMC MODELS IS GOOD WRT THIS WEDGE
PATTERN DEVELOPING BY NEXT WEEKEND SO OVERALL FCST CONFIDENCE IS
IMPROVING. THE PRECIP CHANCES WERE NOT CHANGED MUCH FOR WED WITH A
SLIGHT TO SOLID CHANCE OVER THE CWFA BY EARLY AFTERNOON...HOWEVER I
DID LOWER VALUES FOR THE REST OF THE MEDIUM RANGE TO ACCOUNT FOR THE
STRONGER WEDGE PATTERN. I ALSO REDUCED THE OVERALL QPF EXPECTED FOR
THE EARLY PART OF THE PERIOD. TEMPS WILL START OUT ABOUT A CATEGORY
BELOW NORMAL ON WED AND DROP A FEW MORE DEGREES BY THE WEEKEND. IF
CURRENT MODEL TRENDS CONTINUE AND THE WEDGE IS EXPECTED TO BE EVEN
STRONGER...TEMPS MAY NEED TO BE LOWERED MORE.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
AT KCLT...GUIDANCE SUPPORTS AN MVFR CIG FORMING THIS EVENING...THEN
AN IFR CIG BEFORE DAWN...WITH MVFR VSBY IN FOG BY DAYBREAK...AS
MOISTURE PERSISTS IN THE LOW LEVELS. ALTHOUGH VSBY IMPROVES IN THE
MORNING...CIGS WILL ONLY SLOWLY;Y IMPROVE TO VFR BY MIDDAY. WINDS
WILL FAVOR THE NE. CONVECTIVE CHANCES REMAIN RATHER LIMITED IN
COOL HIGH PRESSURE TO THE NORTH OF A STATIONARY FRONT.

ELSEWHERE...CONVECTIVE CHANCES WILL DIMINISH FORM THE NORTH
OVERNIGHT AS COOL HIGH PRESSURE BUILDS IN FROM THE NORTH. GUIDANCE
FAVORS IFR TO LIFR VSBY IN FOG AT KAVL LATE TONIGHT...WITH MVFR AT
KGSP AND KAND...BUT LEAVES KHKY AND KGMU WITH VFR VSBY. CIG ON THE
OTHER HAND LOWER TO MVFR EVERYWHERE BY DAYBREAK...NOT RETURNING TO
MVFR UNTIL MIDDAY. CONVECTIVE CHANCES WILL IMPROVE FROM THE SOUTH ON
SUNDAY...MAINLY AFTER THIS TAF PACKAGE. WINDS WILL BE FROM THE
NE...EXCEPT AT KAVL...WHERE WINDS ARE EXPECTED TO VEER FROM NW
TONIGHT...TO SE ON SUNDAY.

OUTLOOK...THE WEDGE SHOULD MIX OUT ON MONDAY...BUT SCT
SHOWERS/THUNDERSTORMS WILL DEVELOP AHEAD OF AN APPROACHING COLD
FRONT MONDAY AFTERNOON INTO MONDAY NIGHT. A RETURN TO MAINLY VFR
CONDITIONS IS EXPECTED TUE INTO MIDWEEK OUTSIDE OF RESTRICTIONS WITH
DIURNAL CONVECTION.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH  97%     HIGH  84%     MED   79%     HIGH  84%
KGSP       HIGH  96%     HIGH  89%     HIGH  90%     HIGH  80%
KAVL       HIGH  89%     HIGH  89%     HIGH  87%     HIGH  80%
KHKY       HIGH 100%     HIGH  80%     HIGH  82%     HIGH  84%
KGMU       HIGH  94%     HIGH  89%     HIGH  88%     MED   75%
KAND       HIGH  89%     MED   79%     HIGH  95%     MED   69%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE
HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE
FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JAT/LG
SHORT TERM...PM
LONG TERM...JPT
AVIATION...JAT






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